Positive selection  are represented as__

#Question id: 1369

#Unit 4. Cell Communication and Cell Signaling

The following statements are made with reference to characteristics of glycosaminoglycans and proteoglycans, which are major constituents of extracellular matrix. Which one of them is incorrect?

#Question id: 1370

#Unit 4. Cell Communication and Cell Signaling

H. V. Wilson worked with sponges to gain some insight into exactly what was responsible for holding adjacent cells together. He exposed two species of differently pigmented sponges to a chemical that disrupted intercellular junctions, and the cells of the sponges dissociated. Wilson then mixed the cells of the two species and removed the chemical that caused the cells to dissociate. Wilson found that the sponges reassembled into two separate species. The cells from one species did not interact or form associations with the cells of the other species.

How do you explain the results of Wilson's experiments?

#Question id: 1371

#Unit 4. Cell Communication and Cell Signaling

A researcher was studying a protein ‘A’ which has been observed to move across cells when an extracellular electrical stimulus is provided. An artificial peptide ‘Z’ was prepared which resembles the structure of pannexins and competitively inhibits pannexon formation. Which one of the following statements will best explain the fate of protein ‘A’ if, the cells are treated with peptide ‘Z’ and then, electrical stimulus is provided.

#Question id: 1372

#Unit 4. Cell Communication and Cell Signaling

Match the following junctions (Column I) with their functions (Column II).

#Question id: 1373

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to cholera toxins which can affect the junction’s activity.

a. Toxins produced by Vibrio cholerae, the enteric bacterium that causes cholera, alter the permeability barrier of the intestinal epithelium by altering the composition or activity of gap junctions.

b. Vibrio cholerae also releases a protease that disrupts tight junctions by degrading the extracellular domain of occludin.

c. Toxin-induced changes in tight-junction permeability (increased paracellular transport) and in protein-mediated ion pumping (decreased transcellular transport) can result in massive losses of internal body ions and water into the gastrointestinal tract, which in turn leads to diarrhea and potentially lethal dehydration.

d. Toxin-induced changes in tight-junction permeability (decreased paracellular transport) and in protein-mediated ion pumping (increased transcellular transport) can result in massive losses of internal body ions and water into the gastrointestinal tract, which in turn leads to diarrhea and potentially lethal dehydration.

Which of the following statements are correct?

#Question id: 1374

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to gap junctions.

i. Vertebrate gap junctions are composed of connexins, a family of structurally related transmembrane proteins with molecular weights between 26,000 and 60,000.

ii. Each vertebrate hexagonal particle consists of six noncovalently associated connexin molecules. Each individual connexin molecule has two membrane-spanning α helices with a topology similar to that of claudin.

iii. The permeability of gap junctions is regulated by posttranslational modification of connexins (e.g., phosphorylation) and is sensitive to changes in environmental conditions

such as intracellular pH and Ca2+ concentration, membrane potential, and the intercellular potential between adjacent interconnected cells (“voltage gating”).

iv. The assembly of connexins, their trafficking within cells, and the formation of functional gap junctions apparently depend on N-cadherin and its associated adapter proteins as well as desmosomal proteins.

Which of the following statements are correct?